Sheet feeding apparatus



Aug. 1968 e. DOBSON ETAL 3,395,916

SHEET FEEDING APPARATUS Filed April 19, 1966 2 Sheets-Sheet l mywamv 6w Mf 1 wail) 1968 1. c5. DOBSON ETAL 3,395,916

SHEET FEEDING APPARATUS Filed April 19, 1966 2 Sheets-Sheet 2 3,335316 SHEET FEEDlNG APPARATUS Ian George Dobson and Michael John Anthony Bass, London, England, assignors, by mesne assignments, to Masson Scott 'lhrissell Engineering Limited, London, England, a corporation of England Filed Apr. 19, 1966, Ser. No. 543,735 Claims priority, application Great Britain, Apr. 28, 1965, 17,867/65 7 Claims. (Cl. 271-88) ABSTRAQT OF THE DISCLOSURE A sheet stacking apparatus is provided with an electrically insulated member adjacent one side of the stack being formed on a support; an electric circuit connected between this member and at least one electrically conductive part adjacent at least one other side of the stack produces an output signal representing the capacitance between the member and the conductive parts, and this signal controls the relative heights of sheet delivery and stack support.

This invention relates to sheet feeding apparatus and more particularly to devices for detecting the height of a stack of sheets.

Devices of the sort to which the invention may be applied are especially useful in appartus for feeding and stacking paper sheets, as such apparatus operates at very high speeds and yet the material being handled is readily susceptible of damage. Moreover, when paper sheets are to be fed so as to form a stack, the small weight of each sheet, as related to its area, makes it inadvisable to assume that successive sheets will follow like paths if they are allowed to fall freely for any substantial distance on to the stack being formed.

Accordingly, apparatus (such as paper cutters) which are required to produce a stack of sheets usually includes a device termed a layboy in which the stack is formed, and which essentially includes a platform arranged to carry the stack being formed and means for lowering the platform as sheets are added to the stack to keep the height of the top of the growing stack essentially constant. For a layboy to function efficiently, satisfactory means must be provided to detect the position of the top of the stack.

For this purpose, layboys have been fitted with detectors arranged to project a beam of light over the stack to a photo-electric cell at a predetermined level, so that when the stack grew above that level the beam was broken, and an electric control signal emitted from the cell then served to initiate a platform lowering mechanism. However, such a detector can very readily be operated inadvertently, as anything which interrupts the light beam (cg. an operators hand or arm) produces the same effect as growth of the stack.

It is an object of the present invention to provide an improved device for detecting the position of the top of a stack of sheets, e.g. of paper.

According to the invention, we provide a detecting device for use in a layboy or like apparatus in which a stack is formed from sheets delivered thereto in succession, comprising an electrically conductive plate or the like provided with means for adjustably mounting it in the layboy so as to be electrically insulated from the layboy but adjacent to a side of said stack during its formation, and electric circuit means adapted to be connected to said plate and to electrically conductive parts of the layboy adjacent to one or more other sides of said stack and arranged to deliver an output signal indicative of the capacitance between the said plates and said electrically conduc- States Patent ice tive parts. The invention further comprehends layboys or the like incorporating devices as above set forth.

The output signal provided by such a device affords an indication of the position of the top of the stack, because the capacitance varies with the position of the top of the stack relative to the plate. Assuming for convenience that the electrically conductive parts comprise a wall of the layboy adjacent to the opposite side of the stack from the plate, when the top of the stack is very low the space between the plate or the like and the wall will be empty (more accurately, will be air-filled) while when the top of the stack is very high the space will be full of paper; the capacitance between the plate and the wall will be much greater in the latter condition than in the former, because of the diiference in dielectric constant as between paper and air. When the level of the top of the paper stack is part-way up the plate, so that the space is only partly filled with paper, the capacitance will have a value between those it has in the two extreme cases previously mentioned.

Such a device can equally well be used Where the sheets being handled are of conductive, as opposed to dielectric, material. The operation of the device is slightly different, and it is necessary for the plate to be protected against contact with the stack; for example the plate may have an insulating cover or coating. Preferably in such a case the stack is electrically connected to the aforesaid electrically conductive parts of the apparatus and then as the stack grows, the effect on the capacitance is as if the parts were being moved nearer to the plate; if the stack is electrically isolated, the capacitance sensed will be that produced by two capacitances in series, i.e. the capacitance from the plate to the stack and that from the stack to electrically conductive parts. In either case, the capacitance between the plate and said parts will increase as the stack grows.

(It will be understood that variation of capacitance with stack height only occurs while the top of the stack is within a certain Zone, bounded by horizontal planes approximately at the heights of the lowest and highest parts of the plate.)

The circuit means may be arranged in a variety of ways, according to the manner in which the output signal is desired to be related to the level of the top of the stack. For example, the circuit means may be arranged to deliver three forms of output signal, one indicating that the top of the stack is at a height between two predetermined horizontal planes, and the others indicating that said level is above or below the upper and lower of said planes respectively. The output signals may then be fed to a platform lowering mechanism of an associated layboy in such manner as to control the rate of descent of its platform so that the descent is kept at a normal or average rate while the signal received is in said one form and at a greater or lesser rate while the signal received is of the other respective form.

In a simpler arrangement, which we at present prefer, the platform of the layboy is lowered intermittently, each lowering being initiated when the sensed capacitance exceeds a predetermined value and terminated when said capacitance is reduced to another predetermined and lower value. The sensing device may be arranged to deliver appropriately different output signals when the capacitance sensed is above or below such values respectively or, more simply, to deliver an output signal while the higher predetermined value is exceeded, the platform low ering mechanism then being arranged to operate in response to the output signal and to continue in operation for a suitable fixed time after the signal has ceased. A similar result may be achieved by suitable choice of time constants in the electric circuit means, so that the output signal persists for such a time after the capacitance has fallen. below said value, or a combination of these expedients may be employed.

The use of such a device enables the level of the top of a stack of sheets in a layboy to be maintained constant (within predetermined limits) but the actual level maintained should be readily adjustable as such adjustment is usually required when setting up a machine such as a paper cutter with which the layboy is associated. Such adjustment may be effected in the circuit means but devices embodying the invention have the advantage that such setting up adjustments may more readily be performed by adjustment of the position of the plate.

In forming a stack of sheets of paper, for example, variations in thickness of the paper across the width of the sheets may cause the top of the stack to become curved, e.g. concave, as the height of the stack becomes substantial. In such circumstances, the relationship between stack height and sensed capacitance depends upon where the height is measured and where the plate is mounted, but the fact that the plate is adjustable makes it possible for an operator to alter the level of the top of the stack by simply raising or lowering the plate should curvature of the top of the stack develop. Another important factor is the dielectric constant of the paper; this may vary, even between different parts of a single paper web, but if such variations occur in such a way as to affect the operation of a layboy fitted with a device embodying the invention, the plate may be adjusted to compensate for this.

A layboy usually has a so-called backboard, placed on the opposite side of the layboy from that at which sheets to be stacked are delivered. The backboard serves to stop the sheets and after hitting it each sheet drops on to the stack being formed.

The backboard of a layboy is accordingly an especially convenient place to mount the plate of a device embodying the invention as set forth above, as the device is then well clear of the path of sheets arriving at the layboy for stacking and the plate is therefore readily accessible for adjustment.

For most puposes, the only adjustment of the plate which is required is a vertical adjustment. However, although this may be provided merely by a mounting which allows the plate to slide vertically on the backboard of the layboy, with suitable means for clamping the plate in any desired position of adjustment; this form of mounting necessitates a slot in the backboard if an operator is to be able conveniently to adjust the plate during operation of the layboy. We may therefore provide an eccentrically pivoted plate (i.e., a plate of semi-circular form) pivoted at its centre of curvature, which requires merely a relatively small hole in the backboard to accommodate a supporting shaft extending to an external handle and clamp.

While reference has been and will be made to layboys in which a platform is lowered to maintai nthe level of the top of a stack of sheets thereon substantially constant, it should be noted that devices embodying the invention are equally applicable to layboys in which a stack of sheets is formed on a fixed support, the level at which sheets are delivered to said stack being raised progressively as the stack grows to maintain such level substantially constant relative to the top of the stack. In this case, of course, control signals from the detecting device are applied to sheet feed raising mechanism, in place of the platform lowering mechanism of the other form of layboy.

In order that the invention may be well understood, a preferred embodiment thereof will now be described in some detail, reference being made to the accompanying drawings in which:

FIGURE 1 is a somewhat diagrammatic elevation of a layboy fitted with a detector device embodying the invention;

FIGURE 2 is a section, on a larger scale, on line II-II of FIGURE 1; and

FIGURE 3 is a detail view of a modification.

Referring first to FIGURES 1 and 2, there is shown a layboy generally indicated at 1 and containing a platform 2 carried on a support in the form of the plunger 3 of a hydraulic ram 4. Sheets 5 are delivered to the layboy from one side by conveyor belts 6 and feed rollers 7, said belts and rollers forming part of an associated machine, e.g. a paper cutter.

Supporting bars 8 carry, on the opposite side of the layboy from that at which the sheets 5 arrive, a backboard 9 disposed at such a height as to be struck by sheets 5 delivered by the belts 6 and rollers 7 and serve as a stop for such sheets. The backboard 9 is so placed that sheets stopped thereby fall on to the platform 2 to form a stack 10; a sheet in process of falling on to stack 10 is indicated at all.

The backboard 9 has a central vertically-extending slot 12 (FIGURE 2) in which a block 13 of insulating material is slidably received. An electrically-conductive plate 14 is embedded in the block 13, the surface of block 13 being flush with the inner surface (i.e. the surface facing stack 10) of the backboard 9 on either side of the groove 12. The block 13 is secured to a metal plate 15 which is wider than the slot 12, having lateral edge portions 16 slidably received in grooves in the walls of said slot 12. A terminal T1 connected to the plate 14 extends through (but is insulated from) the plate 15 and a terminal T2 is secured to said plate 15. An inner metal cover 17 secured to plate 15, protects the terminals T1, T2. and an outer cover 18 engages the outer surface of the backboard 9. Inner cover 17' carries a threaded stud 19 extending outward through a hole in outer cover 18 and carrying a clamping nut 20 which when tightened holds the cover 18 against the backboard, thereby securing the whole assembly of block 13, plate 14, plate 15, covers 17, 18 and stud 19. Whenever nut 20 is slackened, said assembly can be moved up or down in the slot 12 of backboard 9 and thereafter retained in any chosen position by re-tightening the nut 20.

Such parts of the structure of the layboy 1 as are of electrically-conductive material, e.g. metal (including platform 2, plunger 3, and a plate 21. bounding the stack 10 on the side adjacent to rollers 7), are electrically grounded.

The terminals T1, T2 are connected by conductors 22, 23 to a detector circuit unit 24 (conductor 23 being grounded within said unit, so that the plate 15 is grounded and thus provides electrical screening for the plate 14). The unit 24 contains electric circuits of any convenient form capable of producing electric output signals on an output line 25 (which may comprise several conductors) to indicate the capacitance existing between the plate 14 and the grounded parts of the layboy. The output signals are delivered to a control unit 26 which is in turn connected by line 27 (which also may comprise several conductors) to a solenoid-operated valve 28 controlling pressure-fluid connections to the hydraulic ram 4.

The exact relationship between the output signals on line 25 and said capacitance is determined by the arrangement of circuits in unit 24 in accordance with the relationship which is desired between said capacitance and the movements of the platform 2 to be produced by the ram 4 under control of the control unit 26 in response to the output signals. One convenient and simple arrangement involves the provision in the unit 24 of a transistor oscillator circuit so connected as to oscillate whenever the capacitance connected to it by conductors 22, 23 is of not less than a preselected magnitude, and having such time constants that oscillation does not cease immediately whenever the capacitance falls below that magnitude. While the oscillator is oscillating, the oscillations are amplified and rectified to provide .a DC. output signal on line 25.

It will be understood that the capacitance to whose magnitude the device responds will increase as the level of the top of the stack rises as the space between plate 14 and grounded pasts of the layboy adjacent to other sides of the stack is increasingly filled with sheets; hence the platform 2 will be required to descend whenever the capacitance reaches the preselected magnitude. The fact that the oscillator does not cease to oscillate as soon as the capacitance is reduced to the preselected magnitude (due to the time constants of the oscillator as aforesaid) leads to the result that each time the platform descends it goes somewhat farther than is necessary to reach the preselected magnitude and this for obvious reasons leads to reasonable intervals between successive descents of the platform 2. The maximum permissible length of these intervals is governed by the greatest spacing which is acceptable from the plane in which the sheets enter the laybay (i.e. the plane of th nip of rollers 7) and the level of he top of the stack 10, as the sheets have to fall through this distance.

The critical setting of the device is that which determines the highest level the top of the stcak 10 can reach before the resultant increase of the aforesaid capacitance causes operation of the device as previously described to lower the platform 2, as the top of stack 10 must be clear of the sheets 10 entering the layboy at all times. Vertical adjustment of the block 13, carrying the plate 14, in groove 12 of backboard 9 allows variation of the level of the top of stack 10 at which the critical capacitance is achieved and hence provides for the critical setting just mentioned.

The presence of the slot 12 in the backboard 9 weakens the latter (which is generally of wood) and suitable reinforcement must be provided which increases the weight and cost of the backboard 9.

The modification illustrated in FIGURE 3 enables a relatively small cylindrical hole in the backboard to replace the slot 12, so that the backboard 9 is not materially weakened.

In FIGURE 3, which is diagrammatic, the backboard 9 carries, in a shallow recess on its inner surface (i.e. the surface facing stack 10) a rotatable disc 29, carried on a shaft extending through the backboard 9 to a suitable handle and clamp (not shown) so that the disc 29 may be manually rotated to any desired position and clamped there by an operator.

The disc 29 is a composite disc, comprising an insulating body 31 in which is set a conductive plate 32, the latter covering approximately one-half of the area of the whole disc 29, having a straight edge connecting with a diameter of the latter.

As drawn in FIGURE 3, the plate 32 is so positioned that its straight edge is horizontal and uppermost, so that the stack 10 would need to rise to the level of the centreline of shaft 30 to cover the whole of plate 32. If however disc 29 is rotated through 90 (in either direction), to bring the straight edge of plate 32 into a vertical plane, then when the top of stack 10 is at the level of the centreline of shaft 30, only one half of the area of plate 32 is covered by the stack, which must rise a further distance (equal to the radius of disc 29) to cover the whole of plate 32 It will be appreciated that rotation of disc 29 raises or lowers plate 32, and hence has the same effect as raising or lowering the plate 14 previously described, and whenever the modification of FIGURE 3 is employed in apparatus otherwise as illustrated in FIGURES 1 and 2, plate 32 may be connected in place of plate 14. It will be noted that a grounded screening plate (corresponding to the plate 15 of FIGURE 2) is desirable and may be fitted behind disc 29, or more conveniently on the rear face of the backboard 9.

The circuits of unit 24 may be adjusted to vary the critical capacitance i.e. the predetermined magnitude at which the device operates. Such setting may be made so that the device operates only when the whole of plate 14 (or 32) is covered by stack 10, when half the plate is so covered, and soon. In connection with the modification shown in FIGURE 3, it is worthy of note that, if the circuits of unit 24 are so adjusted that the device operates when only a small proporiton of the area of plate 32 is covered, then the plate 32 will need to be rotated through a certain minimum angle before such rotation effects any change in the stack level at which operation of the device occurs.

So far reference has been made to a single stack 10. It is however usual for paper cutters or the like and their associated layboys to be of substantial width (measured horizontally at right-angles to the direction of travel of sheets entering the layboy), and for a single stack 10 to be formed only when sheets of maximum width are being made. For a substantial, often major, part of the life of a layboy, sheets of less than maximum width are being made and whenever possible two ore more stacks are formed simultaneously to secure maximum utilisation of equipment. The two or more stacks often grow at different rates, as for various reasons, e.g. the inspection and rejection of faulty sheets, the feed of sheets to the several stacks is not necessarily uniform. in such circumstances it is desirable to arrange that the device described shall operate to lower the platform 2 whenever the top of any one or more of the stacks reaches a predetermined level.

In the simplest modification of the device described, a plate 14, block 13 and slot 12 (or a disc 29 and plate 32) are provided for each stack, and the several plates 14 (or 32) are all connected to line 22. With this arrangement, the operation of the device in relation to the stack heights is in a sense variable; if the device is set to cause platform lowering whenever the top of any one stack reaches the level of the top edge of its associated plate, then if all the stacks grow uniformly the platform will be lowered when the tops of all the stacks are part-way up their respective plates--for two stacks, about half-way up, for three stacks, about one-third of the way up, and so on, assuming that all the plates 14 are set level with one another. The maximum heights which the several stacks may attain may be independently set by adjusting their respective plates to different heights, but in such a case the stack whose associated plate is set lowest will in general control the operation of the device unless there is a tendency for that stack to receive sheets at a lower rate than the other stacks.

If preferred, where a plurality of plates 14 (or 32) are provided, they may have separate connecting lines 22 to the unit 24 and the latter may contain several oscillators, one for each plate, feeding a common amplifier and rectifier; the device will then function to cause lowering of the platform whenever the top of any one of the stacks goes above a predetermined level.

In the foregoing, it has been assumed that when two or more stacks are formed simultaneously, the lengths, (measured in the direction in which the sheets travel to the stack) of the sheets in both or all the stacks are equal. With a duplex machine arranged to provide sheets of different lengths from different parts of a single web, it is of course inescapable that the stack or stacks of short sheets will grow faster than the stack or stacks of long sheets, and hence a duplex layboy, with two independently-operated platforms, is needed, and a separate detecting device is required to control each platform in accordance with the growth of the relevant stack or stacks.

It will be seen that the invention provides a simple but effective and flexible device for the purposes specified and it will be apparent that such devices are capable of a variety of uses. Various changes and modifications of the device described in detail are possible without departure from the scope of the invention, e.g. the plate 14 (or 32) need not be fitted in the position shown but may be to one side of the path of sheets entering the layboy.

What we claim as our invention and desire to secure by Letters Patent is:

1. Apparatus for forming a stack from sheets delivered thereto in succession, comprising a support for the stack being formed, a sheet feed for delivery sheets to form the stack, mechanism for varying the relative levels of said support and said sheet feed, and at least one detecting device comprising an electrically conductive member adjacent to one side of the stack during its formation, said member being adjustably mounted on and electrically insulated from said apparatus, at least one electrically conductive part adjacent to at least one other side of the stack, said member and conductive part being positioned in parallel spaced relation and electric circuit means connected to said member and to each of said conductive parts, said circuit means being arranged to deliver to said mechanism an output signal indicative of the capacitance between said member and at least one of said conductive parts and said mechanism being arranged to respond to said signal by varying the relative levels of the support and the sheet feed as said capacitance increases and decreases respectively so that the relative levels of the sheet feed and the top of the stack are maintained substantially constant.

2. Apparatus as claimed in claim 1, in which the electric circuit means of the detecting device is arranged to supply an output signal serving as a control signal for the mechanism whenever the capacitance exceeds a predetermined value.

3. Apparatus as claimed in claim 2, in which the mechanism is arranged to continue in operation for a fixed time after said output signal has ceased.

4. Apparatus as claimed in claim 2, in which said electric circuit means has such time constants that said output signal persists fora fixed time after the capacitance has fallen below the predetermined value.

5. Apparatus as claimed in claim 1, in which said mechanism is hydraulically operated and comprises at least one hydraulic ram, a solenoid-operated valve, and pressure fluid connections to said ram controlled by said valve, the latter being operable in response to the output signals from the detecting device.

6. Apparatus as claimed in claim 1, in which said support is a movable platform and said mechanism is arranged to lower said platform in response to the output signals from the detecting device.

7. Apparatus as claimed in claim 1, in which the sheet feed can be raised and said mechanism is arranged to raise said sheet feed in response to the output signals from the detecting device.

References Cited UNITED STATES PATENTS RICHARD E. AEGERTER, Primary Examiner. 

